Blade segment and fluid flow machine

ABSTRACT

A blade segment ( 1 ) for a fluid flow machine ( 2 ), including: a first blade ( 3 ); a first shroud ( 7 ) attached to the tip of the first blade ( 3 ) and having a contact face ( 11 ); a second blade ( 3 ′); and a second shroud ( 7 ′) attached to the tip of the second blade ( 3 ′) and having a counter-contact face ( 12 ′) for engagement with the contact face ( 11 ) of the first shroud ( 7 ) in the radial direction (R) in such a way that a friction lock (RF) can be created between the contact face ( 11 ) and the counter-contact face ( 12 ′).

This claims the benefit of European Patent Application EP 101 93 687.0,filed Dec. 3, 2010 and hereby incorporated by reference herein.

The present invention relates to a blade segment and to a fluid flowmachine.

BACKGROUND

It is known, for example, from Japanese Patent Publication JP 2007154695A, to torsionally bias turbine blades. This has a favorable effect onthe damping behavior of the turbine blades during operation thereof. Thetorsional bias is maintained by the turbine blades each being providedon their tips with shrouds that are tied together by Z-shaped interlocknotches, which are also referred to as Z-shrouds.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an alternative orcomplementary approach for coupling at least two blades of a bladesegment so as to achieve a favorable damping behavior.

The present invention provides a blade segment for a fluid flow machine,including: a first blade; a first shroud attached to the tip of thefirst blade and having a contact face; a second blade; and a secondshroud attached to the tip of the second blade and having acounter-contact face for engagement with the contact face of the firstshroud in the radial direction in such a way that a friction lock can becreated between the contact face and the counter-contact face.

Also provided is a fluid flow machine, in particular a turbomachine,having the blade segment according to the present invention.

The present invention can arrange the shrouds of the respective bladesin the manner of roof tiles so that the shrouds rest against each otherin the radial direction in such a way that a friction lock is createdbetween mutually overlapping shrouds at least during operation of theblade segment (or also when it is at rest). The friction lock causes theshrouds, and respectively the blades, to be coupled to each other, whichis favorable in terms of damping behavior.

Advantageous embodiments will become apparent from the dependent claims.

The resting of the contact face against the counter-contact face in theradial direction is understood herein to mean that a vectorperpendicular to the plane in which the contact face and thecounter-contact face rest against each other has at least one radialcomponent.

“Circumferential direction” is understood herein to mean a directionalong a circle whose centerline coincides with the axis of rotation ofthe blade segment in the fluid flow machine. “Radial” is understoodherein to refer to a direction perpendicular to the axis of rotation ofthe blade segment in the fluid flow machine. “Axial” is understoodherein to refer to a direction along the axis of rotation of the bladesegment in the fluid flow machine.

In one embodiment of the blade segment of the present invention, thecenter of gravity of the first shroud is spaced in the circumferentialdirection from a centerline of the first blade in such a way that duringoperation of the blade segment, the first blade bends under the actionof the centrifugal forces so as to create the friction lock between thecontact face and the counter-contact face. Thus, during operation of theblade segment, a bending moment is produced under the action of thecentrifugal forces, said bending moment tending to tilt the bladetogether with the shroud in the circumferential direction. However, suchtilting is prevented by the contact face of the first shroud and thecounter-contact face of the second shroud. In doing so, the contact facepresses radially against the counter-contact face in such a way that afriction lock is created between the contact face and thecounter-contact face.

“Centerline” is understood herein to mean the axis of the first bladethat is positioned in such a way that if the center of gravity of thefirst shroud coincided with this axis, no or only an insignificantbending moment would be introduced from the shroud into the first blade.This applies similarly to the centerline of the second blade.

In one embodiment of the blade segment of the present invention, thecontact face of the first shroud and/or the counter-contact face of thesecond shroud is/are configured with an interference dimension in theradial direction for bending the first blade about its root point in thecircumferential direction to thereby create the friction lock betweenthe contact face and the counter-contact face. The term “interferencedimension” is understood to mean that the contact face and/or thecounter-contact face is/are thickened in the radial direction so as toproduce a contact pressure and, thus, a friction lock between thecontact face and the counter-contact face. This embodiment may beprovided alternatively or in addition to the previous embodiment, wherethe center of gravity of the first shroud is spaced in thecircumferential direction from a centerline of the first blade.

In another embodiment of the blade segment of the present invention, thefriction lock is adapted to produce a reaction torque in a directionabout the centerline of the first and second blades. This is favorablefor the purpose of compensating for the tendency of radially twistedrotor blade airfoils to untwist.

In a further embodiment of the blade segment of the present invention,the first and/or second blade has/have a basic tilt in the axialdirection, which is defined by a basic tilt axis; the contact face andthe counter-contact face being arranged obliquely, in particular at anangle between 45 and 135 degrees, with respect to the basic tilt axis inthe axial direction of the first and second blades. The basic tilt isalso called “lean”. The basic tilt is usually used to allow the gasforces, which occur during the operation of the fluid flow machine andproduce corresponding bending moments on the blades, to be substantiallycompensated for, at least in certain operating ranges of the fluid flowmachine. Depending on the design of the fluid flow machine, the basictilt is typically between 0 and 2 degrees. The oblique arrangement ofthe contact face and the counter-contact face results in a twistingmoment being produced around the centerline of a respective blade, saidtwisting moment being capable of counteracting the untwisting of therespective blade. Here, two mirror-image configurations are possible.This twisting moment increases with the force with which the contactface presses against the counter-contact face.

In another embodiment of the blade segment of the present invention, thecontact and counter-contact faces have an engagement element and areceiving element which engage with one another in the circumferentialdirection. In this manner, the first and second shrouds are supported onone another even better; i.e., in addition to the friction lock. Inparticular, this embodiment prevents untwisting of the blades when nofriction lock is created (for example, when in the embodiment where thecenter of gravity of the shroud is offset in the circumferentialdirection, the blade segment is at rest.)

In a further embodiment of the blade segment of the present invention,the first and/or second blade is/are torsionally biased. When the bladesare in engagement with one another via the aforedescribed engagement andreceiving elements, it is also possible, for example, to torsionallybias the blades such that sufficient coupling between the blades isachieved even at low speeds, which results in a favorable dampingbehavior. At low speeds, the friction lock resulting from the offset ofthe center of gravity of a respective shroud may not suffice to achievesuch a sufficient coupling between the shrouds.

In a further embodiment of the blade segment of the present invention,the first and second blades are rotor blades.

In yet another embodiment of the blade segment of the present invention,the first and second blades are made of a strongly creeping material.“Strongly creeping materials” are understood to be materials which creepmore strongly than current nickel materials.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be described in more detail below withreference to exemplary embodiments and the accompanying drawings, inwhich:

FIG. 1 is a schematic view, looking in the axial direction, of a bladesegment according to an exemplary embodiment of the present invention;

FIG. 2 is a cross-sectional view taken along line A-A in FIG. 1;

FIG. 3 is a cross-sectional view taken along line B-B in FIG. 1;

FIG. 4 is a perspective view of the blade segment of FIG. 1, seenobliquely from below; and

FIG. 5 is a schematic view, looking in the axial direction, of a bladesegment according to another exemplary embodiment of the presentinvention.

DETAILED DESCRIPTION

In the Figures, like reference numerals designate like or functionallyequivalent components, unless stated otherwise.

FIG. 1 schematically shows a blade segment 1 according to an exemplaryembodiment of the present invention, looking in the axial direction.

Blade segment 1 forms part of a fluid flow machine, in particular aturbomachine, which is generally designated by reference numeral 2. Theturbomachine is preferably an aircraft engine.

Blade segment 1 includes two blades 3 and 3′. Blades 3 and 3′ arepreferably rotor blades. Blades 3 and 3′ are mounted by their respectiveroots 4, 4′ in a rotor 5 (see FIG. 4), for example by means of afir-tree connection. Rotor 5 rotates about an axis 6, the blades 3, 3′interacting with a fluid passing through fluid flow machine 2. The termsof “in the circumferential direction”, “in the radial direction” and “inthe axial direction” will be used below with reference to axis 6. Itshould be noted that in reality, axis 6 is significantly further awayfrom blades 3, 3′ than is shown in FIG. 1.

At the radially outer periphery, blades 3, 3′ have shrouds 7, 7′attached to their respective tips. Blades 3, 3′ and their roots 4, 4′and shrouds 7, 7′ are arranged adjacent to each other in circumferentialdirection U, preferably forming a closed ring. The partial view of FIG.1 shows only two such blades 3, 3′. Shrouds 7, 7′ are placed on eachother in the manner of roof tiles in the axial direction.

Shrouds 7, 7′ each have a center of gravity S, respectively S′, which isspaced by a distance D, D′ from a centerline M, M′, of a blade 3, 3′,respectively. Centerlines M, M′ pass through axis 6, which cannot beseen in FIG. 1 because of the highly schematic nature of therepresentation. Further, centerline M passes through a center of gravitySB of blade 3 (see FIG. 2). Center of gravity SB is the center ofgravity of the airfoil of blade 3. This applies similarly to centerlineM′ of blade 3′.

A respective shroud 7, 7′ has a contact face 11, 11′ and an oppositecounter-contact face 12, 12′. Contact faces 11, 11′ and counter-contactfaces 12, 12′ may be formed on respective ends of shrouds 7, 7′ incircumferential direction U.

When blade segment 1 is at rest or rotates at low speed, there are no oralmost no centrifugal forces acting on blades 3, 3′ and their shrouds 7,7′. Blades 3, 3′ and their shrouds 7, 7′ are then in the position thatis shown in FIG. 1 in dashed lines for left blade 3 only. As the speedof blade segment 1 increases, a bending moment of shroud 7 about a rootpoint F of the blade increases as well. This is because center ofgravity S is spaced by distance D from centerline M and center ofgravity SB of blade 3. The resulting bending moment is denoted in FIG. 1by BM. Bending moment BM causes blade 3 to tilt; i.e, bend, along withshroud 7 from its dashed line position to its solid line position inFIG. 1. Above a certain speed, contact face 11 comes into contact withcounter-contact face 12′ in radial direction R, which means that avector 9 (see FIG. 3) perpendicular to plane 10, in which contact face11 and counter-contact face 12′ rest against each other, has at leastone component in radial direction R. As a result, a friction lock iscreated between contact face 11 and counter-contact face 12′. From thispoint on, blade 3 is frictionally coupled to blade 3′, which has afavorable effect on the damping behavior thereof.

FIG. 2 shows a cross-sectional view taken along line A-A in FIG. 1.

In FIG. 2, it can be seen that friction lock RF between contact face 11and counter-contact face 12′ can be created in such a way that itproduces a reaction torque TM about centerline M, which prevents blade 3from oscillating about the centerline in an undesired manner.

FIG. 3 shows a cross-sectional view taken along line B-B in FIG. 1.

As can be seen from FIG. 3, contact face 11 and counter-contact face 12′can be arranged obliquely at an angle W′ of, for example, 93 degreeswith respect to a basic tilt axis G′. The term “obliquely” refers to anangle W′ not equal to 90 degrees and preferably between 45 and 135degrees. Basic tilt axis G′ of blade 3′ may be tilted, for example, 1degree in the direction of axis of rotation 6.

Under the action of centrifugal forces and a corresponding untwisting ofblade 3, a contact force AK is produced between contact face 11 andcounter-contact face 12′. Due to the oblique arrangement of contact face11 and counter-contact face 12′, contact force AK results in a reactionforce RK1 and a reaction force RK2 acting on blade 3. RK2 acts alongbasic tilt axis G′, and RK1 acts perpendicular thereto.

This is also shown in FIG. 2. Here, it can be seen that RK1 produces anadditional twisting moment TR about center of gravity SB and centerlineM of blade 3, which counteracts untwisting E of blade 3.

FIG. 4 shows the blade segment of FIG. 1 in an oblique perspective viewfrom below.

As illustrated in FIG. 4, shrouds 7, 7′ are preferably provided, attheir opposite ends, with engagement elements 13, 13′ and receivingelements 14, 14′ in the region of contact faces 11, 11′ andcounter-contact faces 12, 12′. Engagement element 13′ of shroud 7′engages with receiving element 14 of shroud 7 in the circumferentialdirection. This produces an interlock in the axial direction, whichprevents blades 3, 3′ from untwisting when blade segment 1 is at rest orrotates at low speed, which is when friction lock RF is still too weakto couple blades 3, 3′ to one another.

FIG. 5 schematically shows a blade segment 1 according to anotherexemplary embodiment of the present invention, looking in the axialdirection.

Blade segment 1 differs from that shown in FIGS. 1 through 4 only in themanner in which friction lock RF is created. Apart from that, theexplanations given for FIGS. 1 through 4 apply equally to the bladesegment shown in FIG. 5.

In blade segment 1 of FIG. 5, contact face 11 of shroud 7 is configuredwith an interference dimension P in radial direction R for bending firstblade 3 about its root point F in circumferential direction U to therebycreate friction lock RF between contact face 11 and counter-contact face12′. Of course, the same applies to the other blades of the bladesegment.

In the exemplary embodiment of FIG. 5, friction lock RF is not, or onlyto an insignificant extent, dependent on the speed of rotation.

The embodiments shown in FIGS. 1 through 4 and in FIG. 5 may also becombined with one another.

Although the present invention has been described above with referenceto preferred exemplary embodiments, it is not limited thereto but can bemodified in many ways.

LIST OF REFERENCE NUMERALS

-   1 blade segment-   2 fluid flow machine-   3 blade-   3′ blade-   4 root-   4′ root-   5 rotor-   6 axis of rotation-   7 shroud-   7′ shroud-   9 vector-   10 plane-   11 contact face-   11′ contact face-   12 counter-contact face-   12′ counter-contact face-   13 engagement element-   13′ engagement element-   14 receiving element-   14′ receiving element-   D distance-   F root point-   G′ basic tilt axis-   M centerline-   M′ centerline-   R radial direction-   S center of gravity-   S′ center of gravity-   U circumferential direction-   AK contact force-   BM bending moment-   RF frictional force or lock-   RK1 reaction force-   RK2 reaction force-   SB center of gravity of the blade-   TM reaction torque-   TR twisting moment-   E untwisting

1. A blade segment for a fluid flow machine comprising: a first blade; afirst shroud attached to a tip of the first blade and having a contactface; a second blade; and a second shroud attached to a second tip ofthe second blade and having a counter-contact face for engagement withthe contact face of the first shroud in a radial direction to permitcreation of a friction lock between the contact face and thecounter-contact face.
 2. The blade segment as recited in claim 1 whereina center of gravity of the first shroud is spaced in a circumferentialdirection from a centerline of the first blade, and during operation ofthe blade segment, the first blade bending under action of centrifugalforces to create the friction lock between the contact face and thecounter-contact face.
 3. The blade segment as recited in claim 1 whereinat least one of the contact face of the first shroud and thecounter-contact face of the second shroud is configured with aninterference dimension in the radial direction for bending the firstblade about a root point in a circumferential direction to create thefriction lock between the contact face and the counter-contact face. 4.The blade segment as recited in claim 1 wherein the friction lock isadapted to produce a reaction torque in a direction about a centerlineof at least one of the first and second blades.
 5. The blade segment asrecited in claim 1 wherein at least one of the first and second bladeshas a basic tilt in an axial direction defined by a basic tilt axis, thecontact face and the counter-contact face being arranged obliquely withrespect to the basic tilt axis.
 6. The blade segment as recited in claim5 wherein the contact face and counter-contact face are arrange at anangle between 45 and 135 degrees to the basic tilt axis.
 7. The bladesegment as recited in claim 1 wherein the contact face and thecounter-contact face have an engagement element and a receiving elementengaging one another in a circumferential direction.
 8. The bladesegment as recited in claim 1 wherein at least one of the first andsecond blades is torsionally biased.
 9. The blade segment as recited inclaim 1 wherein the first and second blades are rotor blades.
 10. Theblade segment as recited in claim 1 wherein at least one of the firstand second blades is made of a strongly creeping material.
 11. A fluidflow machine comprising the blade segment as recited in claim
 1. 12. Aturbine comprising the blade segment as recited in claim 1.